feat(smart-app): implement complete mobile app MVP

- App.tsx: full navigation (Auth stack + Main tabs with 5 screens)
- Auth: LoginScreen, RegisterScreen, ForgotPasswordScreen
- HomeScreen: dashboard with IoT metrics, weather widget, alerts, quick actions, sensors
- MapScreen: interactive map with layer toggles (6 layers)
- MarketplaceScreen: categories (6), products (5), search
- ChatScreen: AI chat with quick prompts (4), bot responses
- ProfileScreen: user info, stats, menu (9 items), logout
- AlertsScreen: alert list with severity, acknowledge
- SensorsScreen: sensor list with type filters (6 types), search
- ZonesScreen: zone cards with stats
- SettingsScreen: language picker (FR/EN/ES/DE), privacy, about
- Stores: iotStore (sensors, zones, alerts), notificationStore, uiStore + i18n
- Hooks: useSensors, useAlerts, useNotifications, useLocation
- Components: Card, Button, LoadingSpinner, ErrorBoundary, Header
- Services: iotService, notificationService (with axios API client)
- Utils: formatters (temp, AQI, noise, dates), validators (email, password, IBAN)
- Theme: colors.ts with full design system (Blue Ocean palette)
- Ditto: fixed MongoDB connection, new JWT secrets, official gateway image

smart-app-city/frontend/node_modules/yaml/dist/schema/common/null.js

@@ -0,0 +1,17 @@
+'use strict';
+
+var Scalar = require('../../nodes/Scalar.js');
+
+const nullTag = {
+    identify: value => value == null,
+    createNode: () => new Scalar.Scalar(null),
+    default: true,
+    tag: 'tag:yaml.org,2002:null',
+    test: /^(?:~|[Nn]ull|NULL)?$/,
+    resolve: () => new Scalar.Scalar(null),
+    stringify: ({ source }, ctx) => typeof source === 'string' && nullTag.test.test(source)
+        ? source
+        : ctx.options.nullStr
+};
+
+exports.nullTag = nullTag;